In multi-user communications where a centralized transmitter transmits data to a plurality of independent (e.g., non-cooperative) receivers (users), the transmitted data may be subject to inter-user noise, known as crosstalk, which interferes with the communication between different communication entities. Attaining an effective contrivance to eliminate or at least partially reduce crosstalk is therefore of high importance. Crosstalk may generally occur in both wireless and wire-line communications systems, that utilize linear precoding (LP) and nonlinear precoding (NLP) techniques, and particularly, in the Gigabit Internet “G.fast” wire-line standard.
Crosstalk cancellation techniques that employ precoding of data prior to its transmission are known in the art as “vectoring”. Crosstalk cancellation typically requires taking into account of power restrictions, which often involve hardware-related considerations. Additionally, the number of bits is limited to predefined constellation sizes. The linear precoder may eliminate crosstalk in part or fully by using an inverse of a channel matrix. Linear precoding, however, may typically require equalization of gains introduced by the inversion operation (i.e., the gains must be suppressed to satisfy power restrictions, which in turn cause a diminished bitrate). The NLP schemes avoid this problem by use of Tomlinson-Harashima Precoding (THP) scheme working through the modulus operation or by seeking a perturbation vector associated with transmission symbols, thereby reducing power consumption. NLP schemes work seamlessly at the receiver after application of the modulus operation.
Systems and method that combine linear precoding and nonlinear precoding, in general, are known in the art. A World Intellectual Property Organization (WIPO) Patent Cooperation Treaty (PCT) International Publication Number WO 2014/054043 A1 to Verbin et al. to the same present Applicant, entitled “Hybrid Precoder” is directed to a hybrid precoder system and method employing linear precoding and nonlinear precoding to provide far-end crosstalk (FEXT) cancellation that enhances performance and lowers complexity during transmission and reception of data between transmitters and receivers of the communication system. The hybrid precoder system and method employs linear precoding and non-linear precoding for transmitting data between at least two transmitters and a plurality of receivers via a plurality of communication channels over a plurality of subcarrier frequencies. The at least two transmitters are communicatively coupled, respectively, with the plurality of receivers. The hybrid precoder system includes a linear precoder, a non-linear precoder, a controller, and an input selector. The linear precoder is for linearly precoding the data. The non-linear precoder is for non-linearly precoding the data. The controller is coupled with the linear precoder, and with the non-linear precoder. The input selector as well, is coupled with the linear precoder and with the non-linear precoder. The controller at least partly evaluates channel characteristics of at least part of the communication channels. The controller further determines a precoding scheme selection that defines for at least part of the communication channels, over which of the subcarrier frequencies the data to be transmitted shall be precoded using either one of linear precoding and non-linear precoding, according to determined channel characteristics. The input selector selects which of the linear precoded data and the non-linear precoded data is outputted by the hybrid precoder system, according to the precoding scheme selection.
U.S. Patent Application Publication No.: US 2017/0279490 A1 to Maes, entitled “Non-linear Precoding with a Mix of NLP Capable and NLP Non-capable Lines” is directed at a method for achieving crosstalk mitigation in the presence of nonlinear precoding (NLP) non-capable and NLP capable multiple customer premises equipment (CPE). Maes provides a particular solution to the general interoperability problem of using different precoding-capable CPE units where the number active CPE units, is equal to the total number of CPE units.